The pancreas of a normal healthy person produces and releases insulin into the blood stream in response to elevated blood plasma glucose levels. Beta cells (β-cells), which reside in the pancreas, produce and secrete the insulin into the blood stream, as it is needed. If β-cells become incapacitated or die, a condition known as Type I diabetes mellitus (or in some cases if β-cells produce insufficient quantities of insulin, Type II diabetes), then insulin must be provided to the body from another source.
Traditionally, insulin has been injected with a syringe. More recently, use of infusion pump therapy has been increasing, especially for delivering insulin for diabetics. For example, external infusion pumps are worn on a belt, in a pocket, or the like, and deliver insulin into the body via an infusion tube with a percutaneous needle or a cannula placed in the subcutaneous tissue. As of 1995, less than 5% of Type I diabetics in the United States were using pump therapy, but presently over 25% of the more than 1.12 million Type I diabetics in the U.S. are using infusion pump therapy. Although the infusion pump has improved the way insulin has been delivered, the infusion pump is limited in its ability to replicate all of the functions of the pancreas. Specifically, the infusion pump is still limited to delivering insulin based on user inputted commands and parameters and therefore there is a need to improve the pump to better simulate a pancreas based on current glucose values.